Lignin, a highly abundant natural polymer that can be extracted from biomass, is a polymer of preference for various applications and as a chemical feedstock that replaces petrochemicals. Industrial utilization of lignin is difficult given its variable nature, functionality, reactivity, and heterogeneity. It is desirable to fractionate lignin into stable fractions that have reduced variability in size, composition and reactivity. Fractionation of lignin by membrane filtration using ultrafiltration and nanofiltration membranes results in unstable fractions of lignin that change while being fractionated, and is thus futile. It is also a challenge to characterize the obtained fractions by a reliable method, as chromatography of lignin by size is notoriously dependent on experimental procedure and lack of good standards and suited detectors, and should be considered as relative rather than absolute.
It is the purpose of this invention to prepare thermally stable fractions of high purity lignin by methods that can be applied by industrial means.